VBT and complex geometries.

[ChemSiddiqui]

Hi,

 

I was just wondering why Fe+2 will usually form complexes which have an octahedral geometry while Co+2 will form a tetrahedral complexes. Is there a way from which we can tell that a following metal ion will form what type of complex? Can we use the Valence bond theory to do it?

[amit]

dont know about vbt but cft can sure help in predicting. try any good text book like one by j d lee.

when energy stabalization difference b/w octa and terta is less we can tell. also symmetry is a factor

[ChemSiddiqui]

I am not too sure about what you said there. With cft we will have to assume that the ligands are point charges and as I am sure you will know it not strictly true. Also, I fail to see it having to do anything with geometry because I want to know why Co+2 mostly forms tetrahedral complex while Fe+2 forms octahedral, as both of them have rougly the same electronic configuration.

 

I think I might have to take into account John-Teller distortion?

what u think!

[amit]

jahn taller effect is usually used in explaining diff. bw octahedral and square planer complexes. field splitting (and hence stability) is always greater in octa hedral complexes as tetra hedral complexes have field splitting=4/9 of octahedral.

hence tetra hedral are formed :

1) when ligand is weak so dufference in splitting is not that much.

2)tetra hedral arrangements are symmetrical.

have u consulted any text book? its a question came recently in my university exam. i can write whole ans. but wont it be against sfn's policies of only giving hints

[ChemSiddiqui]

jahn taller effect is usually used in explaining diff. bw octahedral and square planer complexes. field splitting (and hence stability) is always greater in octa hedral complexes as tetra hedral complexes have field splitting=4/9 of octahedral.

hence tetra hedral are formed :

1) when ligand is weak so dufference in splitting is not that much.

2)tetra hedral arrangements are symmetrical.

have u consulted any text book? its a question came recently in my university exam. i can write whole ans. but wont it be against sfn's policies of only giving hints

 

 

fair enough, I am also not looking for the answer!. I just want directions to lead to the answer. I have an inoragnic text but that isnt very useful as far as this question goes. I tried to google it but with no avail. I totally understand your not revealing the answer and i would aslo advise you not to cause i too wouldnt go against the rules. Thanks though!

[amit]

google doesn't have preview of the book from where i read.

there are 6 factors given, i wont explain them (short of time and money to spend on internet)

size of ligand,

configuration(d0,d2,d5,d7,d10 are symetric in tetra as it have 2 orbitals of low energy 3 of higher one against octa where its vise versa,

strength of ligand,

oxidation state of central metal ion(low state low field splitting)

loss of cfse(crystal field stabelization energy) is small eg d1, d6 states loss of cfse=.13 of octahedral

also halides (except f) prefer tetra

page 221 ,coincise inorganic chemistry

j d lee

read this text it will lift the curtains of ignorance from your eyes!

[ChemSiddiqui]

j d lee, well its not the book we are recommended here in the Uk, usually its housecroft and Shrape which is used in most universities. I will try to work out the answer to it myself and from the points you mentioned up there. I did consider some of the points but hopefully I will crack it up fully!. Thanks for your help amit.